Numerous plasticizers are used in formulating vinyl plastics, such as polyvinyl chloride. Due to the diversity of end-use applications of these plastic materials, no single plasticizer can provide the necessary balance of physical properties for all end-use applications.
Simple esters based on trimellitic anhydride, such as tri(2-ethylhexyl) trimellitate, are known and have been demonstrated to be effective plasticizers for polyvinyl chloride. Other simple trimellitate esters are described by Paul C. Dougherty et al, in his article entitled "Vinyl Plasticizers from Trimellistic Anhydride" found in Technical Papers, Volume VIII, presented at the Eighteenth Annual Technical Conference of the SPE in January, 1962. Related compounds, such as esters of cyclohexane-1,2,4-tricarboxylic acid and trialkyl esters of trimesic acid, have also been suggested as plasticizers for vinyl chloride polymers in U.S. Pat. Nos. 3,444,237 and 3,043,792, respectively.
In spite of the fact that use of the trimellitate plasticizers has grown at a rapid rate since their introduction, these plasticizers are not without certain disadvantages which limit their use. While the trimellitate plasticizers are generally considered to have satisfactory volatility, good low temperature performance characteristics and low viscosity, they are easily extracted by hydrocarbons such as hexane and oils. The inability of the trimellitate plasticizers to withstand hydrocarbon extraction precludes their use in automotive applications, such as ignition wiring insulation, where ordinarily these plasticizers would be extremely useful due to their ability to be readily compounded with polyvinyl chloride and the otherwise desirable properties they give to the extrudate.
It would be desirable and advantageous if trimellitate plasticizers having enhanced resistivity to hydrocarbon extraction were available. It would be even more advantageous if these improved trimellitate plasticizers could be easily prepared and were relatively low cost materials.